Boxster 986 - No high beams, really strange symptoms.

[particlewave]

The failure of the headlight switch can be caused by pitting and carbon buildup on the contacts (they can also just fall apart).
This causes high resistance/low current flow through the contacts, meaning that you can get 12V at the other end, but it is very low current. Apply a load and the contacts cannot supply enough current to power the load. A multimeter has very low load, which is why you are getting a voltage reading with it.

The switches can be cleaned easily as I noted above. Go pick up a $5 can of contact cleaner and give it a try.

It's going to be either the headlight or ignition switch (don't forget to check the wiring inside the headlight as suggested).

[Shandy]

Originally Posted by particlewave

The failure of the headlight switch can be caused by pitting and carbon buildup on the contacts (they can also just fall apart).
This causes high resistance/low current flow through the contacts, meaning that you can get 12V at the other end, but it is very low current. Apply a load and the contacts cannot supply enough current to power the load. A multimeter has very low load, which is why you are getting a voltage reading with it.

The switches can be cleaned easily as I noted above. Go pick up a $5 can of contact cleaner and give it a try.

It's going to be either the headlight or ignition switch (don't forget to check the wiring inside the headlight as suggested).

Thanks. I'm dropping the car off tomorrow for Variocam tensioner pads so will buy some contact cleaner and try cleaning the switch when I get the car back from the garage.

So, just to clarify, you mean to try cleaning the circular headlamp switch in the dashboard (not the stalk control)? I did check the wiring in the headlights themselves, all looks good. I actually tried applying 12v directly to the various headlight terminals/pins themselves when out of the car and all lamps worked correctly. I used a wiring diagram you posted a while back to identify the correct pins so thanks for that!

The really confusing thing is that the full beam dashboard light illuminates when the headlamp units are both out of the car and I push or pull the stalk control...